Digital terrain modelling of drainage channel erosion

Drainage channels constructed on highly erodible soils in some areas of Southern Navarre during 1988 have undergone severe erosion, including bed and bank degradation. This erosion triggered lateral gully development that affected adjacent cultivated fields. These processes are similar to those observed in permanent gullies in the area. One severely eroded channel representative of the area was selected for further examination. The amount of erosion was determined by comparing the initial size of the drainage channel with its present condition using digital terrain models and a terrain representation system. Results show that average soil losses along the eroded reach are 3.62 m(3)/m, highlighting the necessity of using improved design methods. Current simulation models can aid in determining such design criteria. If drainage channels are to be constructed in areas of highly erodible soils, they should be shorter and restricted to the lower regions of the watersheds with gentler slopes. Sudden changes in bed slope should be avoided, and adequate erosion control techniques within the channel should be considered. The measurement method used provides detailed information on channel erosion processes with a reasonable effort. (C) 1999 Silsoe Research Institute.